1. Field of the Invention
The invention relates to pole wheels and more particularly to an improved pole wheel having a hollow magnet body and a retaining part;
2. Description of the Prior Art
European Patent Disclosure EP 0 601 228 B1, a pole wheel, a first component that is produced in the form of a hollow magnet body of magnetic powder with thermoplastic binder, has at least one north pole and one south pole in the circumferential direction, and surrounds a shaft in a manner free of tensile and compressive stress, and a second component, which is a retaining part of thermoplastic material seated solidly on the shaft and axially adjoins the first component, and positive engagement connecting means for retaining the hollow magnet body axially and in a manner secure against relative rotation on the retaining part; the positive engagement connecting means being embodied integrally with one of the two components. The retaining part is the component that is embodied integrally with the positively acting connecting means; the connecting means are embodied on the order of spring tongues and each has a hooklike end. In practice, two such connecting means are disposed diametrically opposite one another. The hollow magnet body has an inner diameter such that it surrounds the shaft and is free of tensile stresses and compressive stresses. This is achieved by using a clearance fit or so-called sliding fit. Beginning at the inside diameter, the hollow magnet body has two longitudinal grooves, through which the hooklike ends of the connecting means are moved when the two components are put together, after which the hooklike ends grip on the face end next to the hollow magnet body, while the other zones of the connecting means rest, yielding radially outward, in the grooves. In this way, a bidirectional axial securing to the retaining part as well as securing against relative rotation relative to the retaining part are attained. It can be seen that to pass the hooklike ends through the grooves and to introduce the connecting means into the grooves, a rotational alignment that must be performed by hand or in some other way is required.
From later-published German Patent Disclosure DE 198 23 648 A1, a hollow magnet body acting as a pole wheel is known which is embodied in slit form in the region of one end and which around the slit end has an annular auxiliary body, which acts like a bandage and for that purpose is of metal. This annular auxiliary body takes on the task of pressing the slit end against a shaft. Next to the slit end, the hollow magnet body surrounds the shaft with radial play. There, along the radial play, the hollow magnet body in the state of repose is free of compressive and tensile stresses, so that only stresses caused by centrifugal force act on the material comprising the hollow magnet body.
The characteristics of the invention have the summary that in a simple way, an injection molding operation that is required anyway for the hollow magnet body inside an injection mold simultaneously brings about the positive engagement union with the already-produced retaining part that has been introduced into the injection mold. As a result, the magnet body rests over a large area and without play on the retaining part. The retaining part forms a kind of hub for the hollow magnet body. Injection molding the hollow magnet body onto the retaining part makes it unnecessary to embody the connecting means in the form of resilient tongues and in this way simplifies the choice of material from which the retaining part is made.
In accordance with one embodiment the connecting means generated by injection molding are partly visible and can be monitored by visual checking as to whether an adequate positive engagement between the connecting means and the retaining part has been attained by means of the injection molding operation.
It is possible to produce injection mold cores for the injection tool intended to produce the retaining part with recourse to manufacturing devices and manufacturing means for conventionally embodied mold drafts. This makes it possible to produce the injection mold for the retaining part economically. Improved positive engagement may be obtained by means of additional mold drafts.
In one embodiment of the finished in the finished combination of the retaining body with the hollow magnet body, a bleb remains, which can be broken off in a reliable way inside the outer contour of the pole wheel, so that no problematic protrusion past the pole wheel will thus exist.
A balanced pole wheel maybe created using two injection nozzles for the material of the magnet body; the collar with its two alignment faces is the aid with which the indentations can be made in the retaining part in the alignments relative to the injection nozzles. The collar with the two parallel alignment faces, which can be used in the manner of tool faces of screws, also attains the further advantage, however, of an additional rotational slaving when the magnet body is driven by means of the retaining part. The collar has still another advantage, that it reinforces the radial securing of the hollow magnet body relative to the retaining part that is effected by means of the connecting means that are put in place by positive engagement.